TypeScript union members in a function return value highlighted inconsistently

JavaScript and TypeScript Nightly version: 5.9.20250330

When returning a union from a function in TypeScript, the first member of the union is rendered inconsistently.

export function myFunction():
  | null
  | null
  | null {
  return null;
}

The first | is rendered as mtk5 while the other ones are rendered as mtk1. This is an issue for color themes where both are rendered differently (e.g. the default Monokai theme). Similarily, the first null value is rendered as mtk17 while the other ones are rendered as mtk16.

This might be the same bug as #997. #1043 and #1041 also seem related.

Start with the TypeScript TextMate grammar used to tokenize the provided union-return example, then compare how the first and subsequent | and null tokens are classified. Reproduce the inconsistent scopes with the sample and confirm that the relevant grammar change gives all equivalent union members consistent highlighting without regressing the related cases in #997, #1043, and #1041.